Vortex pump

ABSTRACT

An impeller may include a blade groove region disposed in an outer circumferential portion of at least one end surface of two end surfaces in a rotation axis direction, the blade groove region including a plurality of blades and a plurality of blade grooves. The blade groove may be disposed between adjacent blades, open at one end surface side, and closed at the other end surface side. A housing of the pump includes an opposing groove opposing the blade groove region and extending along the rotation direction of the impeller. A rate of a depth of the opposing groove at an intermediate position excluding both ends of the opposing groove in the rotation direction of the impeller to a depth of each of the blade grooves at the deepest position of the each of the blade grooves may be equal to or less than 0.7.

TECHNICAL FIELD

The disclosure herein relates to a vortex pump that pumps a gas. The vortex pump may also be called a Wesco pump, a cascade pump, or a regenerative pump.

BACKGROUND ART

Japanese Utility Model Application Publication No. H5-73287 (U) describes a vortex pump that supplies a pressurized fuel to a fuel injector in a vehicle. The vortex pump includes an impeller including a plurality of blades on its outer circumferential portion and a housing that houses the impeller. A fluid passage is formed around the blades of the impeller by the housing and the impeller.

SUMMARY Technical Problem

In the vortex pump, a vortex (which is also called swirling flow) about a center axis along a rotation direction of the impeller is generated by rotation of the impeller in a fluid inside the fluid passage to pressurize and the fluid is discharged. In the disclosure herein, a technique that improves a pump efficiency in a vortex pump that pumps a gas is provided.

Solution to Problem

The disclosure herein discloses a vortex pump that pumps a gas. The vortex pump may comprise a housing comprising a suction channel and a discharge channel; and an impeller housed in the housing and configured to rotate about a rotation axis. The impeller may comprise a blade groove region disposed in an outer circumferential portion of at least one end surface of two end surfaces in a rotation axis direction, the blade groove region including a plurality of blades and a plurality of blade grooves, each of the plurality of blade grooves being disposed between adjacent blades. Each of the plurality of blade grooves may be open at one end surface side, and may be closed at the other end surface side. The housing may comprise an opposing groove opposing the blade groove region and extending along the rotation direction of the impeller. A rate of a depth of the opposing groove at an intermediate position excluding both ends of the opposing groove in the rotation direction of the impeller to a depth of each of the blade grooves at the deepest position of the each of the blade grooves may be equal to or less than 0.7.

The inventors discovered that when the rate of the depth of the opposing groove at the intermediate position excluding the both ends of the opposing groove in the rotation direction of the impeller to the depth of each of the blade grooves at the deepest position of the each of the blade grooves is set to equal to or less than 0.7, the pump efficiency of the vortex pump is improved. According to the above configuration, the pump efficiency of the gas vortex pump may be improved.

The disclosure herein discloses another vortex pump configured to pump a gas. The vortex pump may comprise a housing comprising a suction channel and a discharge channel; and an impeller housed in the housing and configured to rotate about a rotation axis. The impeller may comprise a blade groove region disposed in an outer circumferential portion of at least one end surface of two end surfaces in a rotation axis, the blade groove region including a plurality of blades and a plurality of blade grooves, each of the plurality of blade grooves disposed between adjacent blades along a rotation direction of the impeller. Each of the plurality of blade grooves may be open at one end surface side, and may be closed at the other end surface side. The housing may comprise an opposing groove opposing the blade groove region and extending along the rotation direction of the impeller. A rate of a depth of the opposing groove at an intermediate position excluding both ends of the opposing groove in the rotation direction of the impeller to a depth of each of the blade grooves at the deepest position of the each of the blade groove may be set such that a center of a vortex generated by the respective blade grooves and the opposing groove while the impeller rotates is located inside the each of the blade grooves.

In the vortex pump, as the impeller rotates, a vortex about its center axis along the rotation direction of the impeller is generated in the space formed by the blade grooves of the impeller and the opposing groove of the housing. The inventors discovered that the pump efficiency may be improved when a center of the vortex is located in the blade grooves. As a reason why the pump efficiency is improved, when seen in a cross-sectional view that perpendicularly intersects the rotation of the impeller, a vicinity of the center of the vortex has a low gas pressure as compared to an outer circumferential end of the vortex. As a result, when seen in the perpendicularly-intersecting cross sectional view, a flow is generated in the gas from a high-pressure side to a low-pressure side, that is, from the vicinity of the outer circumferential end of the vortex toward the vicinity of the center.

The pressure of the gas in the space formed by the blade grooves of the impeller and the opposing groove of the housing increases as the impeller rotates. That is, the pressure of the gas in the space formed by the blade grooves of the impeller and the opposing groove of the housing increases as the gas progresses in the rotation direction of the impeller. Due to this, if the center of the vortex is located outside the blade grooves, the gas in the vicinity of the center flows toward the low-pressure side, that is, inverse to the rotation direction of the impeller. As a result, when the center of the vortex is located outside the blade grooves, the pump efficiency is reduced. On the other hand, when the center of the vortex is located inside the blade grooves, the gas in the vicinity of the center is prevented from flowing back by the blades located on the opposite side from the blade grooves in the rotation direction of the impeller. Due to this, backflow of the gas is suppressed, and the pump efficiency can be improved.

The inventors considered the structure of the vortex pump from the above viewpoint, and further discovered that the center position of the vortex moves when the depth of the opposing groove is changed relative to the depth of the blade grooves. As a result of further studies, the inventors discovered that the center of the vortex is substantially located in the blade grooves when the rate of the depth of the opposing groove to the depth of the blade grooves is set to equal to or less than 0.7, which increases a discharge flow rate of the fluid as compared to a case where the rate is greater than 0.7.

A rate of a width of each of the blade grooves to a distance from a bottom edge of the each of the blade grooves to a bottom edge of the opposing groove in a cross sectional view passing through the rotation axis of the impeller and the deepest position of the each of the blade grooves may be equal to or more than 0.8 and equal to or less than 1.0. According to this configuration, a shape of the vortex in the perpendicularly-intersecting cross sectional view may become closer to being circular. As a result, the vortex may be flown smoothly within the aforementioned numerical range, and the pump efficiency may thereby be improved.

In the cross sectional view passing through the rotation axis of the impeller and the deepest position of the each of the blade grooves, the rate of the depth of the opposing groove to the depth of the each of the blade grooves may be equal to or more than 0.4 and equal to or less than 0.7, and the rate of the width of the each of the blade grooves to a distance from a bottom edge of the each of the blade grooves to a bottom edge of the opposing groove may be equal to or more than 0.8 and equal to or less than 1.1. According to this configuration, the shape of the vortex in the perpendicularly-intersecting cross sectional view can become closer to being circular. As a result, the vortex can be flown smoothly within the aforementioned numerical range, and the pump efficiency can thereby be improved.

The impeller may comprise an outer circumferential wall at an outer circumferential edge, wherein the outer circumferential wall closes the plurality of the blade grooves at an outer circumferential side of the impeller. According to this configuration, the gas flowing toward the outer circumferential direction of the impeller may be guided in a swirling direction of the vortex by the outer circumferential wall.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a schematic configuration of a fuel supply system of a vehicle of an embodiment.

FIG. 2 shows a perspective view of a purge pump of the embodiment.

FIG. 3 shows a cross-sectional view of a cross section of FIG. 2.

FIG. 4 shows a plan view of an impeller of the embodiment.

FIG. 5 shows a bottom surface view seeing a cover of the embodiment from below.

FIG. 6 shows an enlarged view of a region AR of FIG. 3.

FIG. 7 shows a simulation result showing a relationship of an opposing groove depth/blade groove depth and a flow rate.

FIG. 8 shows a simulation result showing a relationship of a channel width/channel height and the flow rate.

FIG. 9 shows a simulation result showing a relationship of the opposing groove depth/blade groove depth and the channel width/channel height and the flow rate.

FIG. 10 shows a simulation result of a vortex in a case where the opposing groove depth/blade groove depth is 0.6 and the channel width/channel height is 1.0.

FIG. 11 shows a simulation result of the vortex in a case where the opposing groove depth/blade groove depth is 0.8 and the channel width/channel height is 1.0.

FIG. 12 shows a simulation result of the vortex in a case where the opposing groove depth/blade groove depth is 0.8 and the channel width/channel height is 0.8.

FIG. 13 shows a simulation result of a flow in a vicinity of a center of the vortex in the case where the opposing groove depth/blade groove depth is 0.6 and the channel width/channel height is 1.0.

FIG. 14 shows a simulation result of a flowing direction in the case where the opposing groove depth/blade groove depth is 0.8 and the channel width/channel height is 0.8.

FIG. 15 shows a perspective view of an impeller of a variant.

DETAILED DESCRIPTION

A purge pump 10 of an embodiment will be described with reference to the drawings. As shown in FIG. 1, the purge pump 10 is mounted in a vehicle, and is arranged in a fuel supply system 1 that supplies fuel stored in a fuel tank 3 to an engine 8. The fuel supply system 1 includes a main supply passage 2 and a purge supply passage 4 for supplying the fuel from the fuel tank 3 to the engine 8.

The main supply passage 2 includes a fuel pump unit 7, a supply pipe 70, and an injector 5 arranged thereon. The fuel pump unit 7 includes a fuel pump, a pressure regulator, a control circuit, and the like. In the fuel pump unit 7, the control circuit controls the fuel pump according to a signal supplied from an ECU (abbreviation of Engine Control Unit) 6 to be described later. The fuel pump pressurizes and discharges the fuel in the fuel tank 3. The fuel discharged from the fuel pump is regulated by the pressure regulator, and is supplied from the fuel pump unit 7 to the supply pipe 70.

The supply pipe 70 communicates the fuel pump unit 7 and the injector 5. The fuel supplied to the supply pipe 70 flows in the supply pipe 70 to the injector 5. The injector 5 includes a valve of which aperture is controlled by the ECU 6. When this valve is opened, the injector 5 supplies the fuel supplied from the supply pipe 70 to the engine 8.

The purge supply passage 4 is provided with a canister 73, a purge pump 10, a VSV (abbreviation of Vacuum Switching Valve) 100, and communicating pipes 72, 74, 76, 78 communicating them. The canister 73 absorbs vaporized fuel generated in the fuel tank 3. The canister 73 includes a tank port, a purge port, and an open-air port. FIG. 1 shows a flowing direction of the gas in the purge supply passage 4 and the suction pipe 80 by arrows. The tank port is connected to the communicating pipe 72 extending from an upper end of the fuel tank 3. Due to this, the canister 73 is communicated with the communicating pipe 72 extending from the upper end of the fuel tank 3. The canister 73 accommodates an activated charcoal capable of absorbing the fuel. The activated charcoal absorbs the vaporized fuel from gas that enters into the canister 73 from the fuel tank 3 through the communicating pipe 72. The gas that had flown in to the canister 73 passes through the open-air port of the canister 73 after the vaporized fuel has been absorbed, and is discharged to open air. Due to this, the vaporized fuel can be suppressed from being discharged to open air.

The purge port of the canister 73 connects to the purge pump 10 via the communicating pipe 74. Although a detailed structure will be described later, the purge pump 10 is a so-called vortex pump that pressure-feeds gas. The purge pump 10 is controlled by the ECU 6. The purge pump 10 suctions the vaporized fuel absorbed in the canister 73 and pressurizes and discharges the same. During when the purge pump 10 is driving, air is suctioned from the open-air port in the canister 73, and is flown to the purge pump 10 together with the vaporized fuel.

The vaporized fuel discharged from the purge pump 10 passes through the communicating pipe 76, the VSV 100, and the communicating pipe 78, and flows into the suction pipe 80. The VSV 100 is an electromagnetic valve controlled by the ECU 6. The ECU 60 controls the VSV 100 for adjusting a vaporized fuel amount supplied from the purge supply passage 4 to the suction pipe 80. The VSV 100 is connected to the suction pipe 80 upstream of the injector 5. The suction pipe 80 is a pipe that supplies air to the engine 8. A throttle valve 82 is arranged on the suction pipe 80 upstream of a position where the VSV 100 is connected to the suction pipe 80. The throttle valve 82 controls an aperture of the suction pipe 80 to adjust the air flowing into the engine 8. The throttle valve 82 is controlled by the ECU 6.

An air cleaner 84 is arranged on the suction pipe 80 upstream of the throttle valve 82. The air cleaner 84 includes a filter that removes foreign particles from the air flowing into the suction pipe 80. In the suction pipe 80, when the throttle valve 82 opens, the air is suctioned from the air cleaner 84 toward the engine 8. The engine 8 internally combusts the air and the fuel from the suction pipe 80 and discharges exhaust after the combustion.

In the purge supply passage 4, the vaporized fuel absorbed in the canister 73 can be supplied to the suction pipe 80 by driving the purge pump 10. In a case where the engine 8 is running, a negative pressure is generated in the suction pipe 80. Due to this, even in a state where the purge pump 10 is at a halt, the vaporized fuel absorbed in the canister 73 is suctioned into the suction pipe 80 by passing through the halted purge pump 10 due to the negative pressure in the suction pipe 80. On the other hand, in cases of terminating idling of the engine 8 upon stopping the vehicle and running by a motor while the engine 8 is halted as in a hybrid vehicle, that is, in other words in a case of controlling an operation of the engine 8 in an ecofriendly mode, a situation arises in which the negative pressure in the suction pipe 80 by the operation of the engine 8 is hardly generated. In such a situation, the purge pump 10 can supply the vaporized fuel absorbed in the canister 73 to the suction pipe 80 by taking over this role from the engine 8. In a variant, the purge pump 10 may be driven to suction and discharge the vaporized fuel even in the situation where the engine 8 is running and the negative pressure is being generated in the suction pipe 80.

Next, a configuration of the purge pump 10 will be described. FIG. 2 shows a perspective view of the purge pump 10 as seen from a pump unit 50 side. FIG. 3 is a cross sectional view showing a cross section of FIG. 2. Hereinbelow, “up” and “down” will be expressed with an up and down direction of FIG. 3 as a reference, however, the up and down direction of FIG. 3 may not be a direction by which the purge pump 10 is mounted on the vehicle.

The purge pump 10 includes a motor unit 20 and a pump unit 50. The motor unit 20 includes a brushless motor. The motor unit 20 is provided with an upper housing 26, a rotor (not shown), a stator 22, and a control circuit 24. The upper housing 26 accommodates the rotor, the stator 22, and the control circuit 24. The control circuit 24 converts DC power supplied from a battery of the vehicle to three-phase AC power in U phase, V phase, and W phase, and supplies the same to the stator 22. The control circuit 24 supplies the power to the stator 22 according to a signal supplied from the ECU 6. The stator 22 has a cylindrical shape, at a center of which the rotor is arranged. The rotor is arranged rotatable relative to the stator 22. The rotor includes permanent magnets along its circumferential direction, which are magnetized alternately in different directions. The rotor rotates about a center axis X (called a “rotation axis X” hereinafter) a shaft 30 by the power being supplied to the stator 22.

The pump unit 50 is arranged below the motor unit 20. The pump unit 50 is driven by the motor unit 20. The pump unit 50 includes a lower housing 52 and an impeller 54. The lower housing 52 is fixed to a lower end of the upper housing 26. The lower housing 52 includes a bottom wall 52 a and a cover 52 b. The cover 52 b includes an upper wall 52 c, a circumferential wall 52 d, a suction port 56, and a discharge port 58 (see FIG. 2). The upper wall 52 c is arranged at the lower end of the upper housing 26. The circumferential wall 52 d protrudes from the upper wall 52 c downward, and surrounds an outer circumference of a circumferential edge of the upper wall 52 c. The bottom wall 52 a is arranged at a lower end of the circumferential wall 52 d. The bottom wall 52 a is fixed to the cover 52 b by bolts. The bottom wall 52 a closes the lower end of the circumferential wall 52 d. A space 60 is defined by the bottom wall 52 a and the cover 52 b.

FIG. 5 is a diagram seeing the cover 52 b from below. The circumferential wall 52 d has the suction port 56 and the discharge port 58 which respectively communicates with the space 60 protruding therefrom. The suction port 56 and the discharge port 58 are arranged parallel to each other and perpencicular to the up and down direction. The suction port 56 communicates with the canister 73 via the communicating pipe 74. The suction port 56 includes a suction channel therein, and introduces the vaporized fuel from the canister 73 into the space 60. The discharge port 58 includes a discharge channel therein, communicates with the suction port 56 in the lower housing 52, and discharges the vaporized fuel suctioned into the space 60 to outside the purge pump 10.

The upper wall 52 c includes an opposing groove 52 e extending along the circumferential wall 52 d from the suction port 56 to the discharge port 58. The bottom wall 52 a similarly includes an opposing groove 52 f extending along the circumferential wall 52 d from the suction port 56 to the discharge port 58 (see FIG. 3). The opposing grooves 52 e and 52 f each have a constant depth at an intermediate position, which is more specifically at the position facing the impeller 54, and become gradually shallower at each of both ends in a longitudinal direction. When seen along a rotation direction R of the impeller 54, the discharge port 58 and the suction port 56 are separated by the circumferential wall 52 d. Due to this, the gas is suppressed from flowing from the high-pressure discharge port 58 to the low-pressure suction port 56.

As shown in FIG. 3, the space 60 accommodates the impeller 54. The impeller 54 has a circular disk-like shape. A thickness of the impeller 54 is somewhat smaller than a gap between the upper wall 52 c and the bottom wall 52 a of the lower housing 52. The impeller 54 opposes each of the upper wall 52 c and the bottom wall 52 a with a small gap in between. Further, a small gap is provided between the impeller 54 and the circumferential wall 52 d. The impeller 54 includes a fitting hole at its center for fitting the shaft 30. Due to this, the impeller 54 rotates about the rotation axis X accompanying rotation of the shaft 30.

As shown in FIG. 4, the impeller 54 includes a blade groove region 54 f, which includes a plurality of blades 54 a and a plurality of blade grooves 54 b, at an outer circumferential portion of its upper surface 54 g. In the drawings, reference signs are given only to one blade 54 a and one blade groove 54 b. Similarly, the impeller 54 further includes a blade groove region 54 f, which includes a plurality of blades 54 a and a plurality of blade grooves 54 b, at an outer circumferential portion of its lower surface 54 h. The upper surface 54 g and the lower surface 54 h can be termed end surfaces of the impeller 54 in the rotation axis X direction. The blade groove region 54 f arranged in the upper surface 54 g is arranged opposing the opposing groove 52 e. Similarly, the blade groove region 54 f arranged in the lower surface 54 h is arranged opposing the opposing groove 52 f. Each of the blade groove regions 54 f surrounds the outer circumference of the impeller 54 in the circumferential direction at an inner side of the outer circumferential wall 54 c of the impeller 54. The plurality of blades 54 a each has a same shape. The plurality of blades 54 a is arranged at an equal interval in the circumferential direction of the impeller 54 in each blade groove region 54 f. One blade groove 54 b is arranged between two blades 54 a that are adjacent in the circumferential direction of the impeller 54. That is, the plurality of blade grooves 54 b is arranged at an equal interval in the circumferential direction of the impeller 54 in on the inner side of the outer circumferential wall 54 c of the impeller 54. In other words, each of the plurality of blade grooves 54 b has its end on an outer circumferential side closed by the outer circumferential wall 54 c.

FIG. 6 is an enlarged view of a region AR of FIG. 3, and shows a cross sectional view passing through the rotation axis X (that is, including the rotation axis X) and being at the deepest position of the blade grooves 54 b arranged on both surfaces of the impeller 54. As shown in FIG. 6, each of the plurality of blade grooves 54 b arranged on the lower surface 54 h of the impeller 54 is open on a lower surface 54 h side of the impeller 54, and is closed on an upper surface 54 g side of the impeller 54. Similarly, each of the plurality of blade grooves 54 b arranged on the upper surface 54 g of the impeller 54 is open on the upper surface 54 g side of the impeller 54, and is closed on the lower surface 54 h side of the impeller 54. That is, the plurality of blade grooves 54 b the arranged on the lower surface 54 h of the impeller 54 and the plurality of blade grooves 54 b arranged on the upper surface 54 g of the impeller 54 are separated, and are not communicated.

During when the purge pump 10 is driving, the impeller 54 is rotated by the rotation of the motor unit 20. As a result, a gas containing the vaporized fuel absorbed in the canister 73 is suctioned from the suction port 56 into the lower housing 52. A vortex of the gas (swirling flow thereof) is generated in a space 57 formed by the blade grooves 54 b and the opposing groove 52 e. The same applies to a space 59 formed by the blade grooves 54 b and the opposing groove 52 f. As a result, the gas in the lower housing 52 is pressurized, and is discharged from the discharge port 58.

Next, results of simulations carried out using the purge pump 10 will be shown with reference to FIGS. 7 to 9. In the simulations, the pump unit 50 of the purge pump 10 was modelized, and the flow rate of the gas discharged from the discharge port 58 when the impeller 54 is rotated was calculated. A revolution speed of the impeller 54 was set constant, and energy inputted to the pump unit 50 was substantially set constant

In the simulations, the discharge flow rate for cases of changing a rate D2/D1 of an opposing groove depth D2 relative to a blade groove depth D1 and a rate W/H of a channel width W relative to a channel height H as shown in FIG. 6 was calculated. In a case where the discharge flow rate is relatively large under a situation in which the input energy to the pump unit 50 is constant, this can be said as that the pump efficiency is high, and in a case where the discharge flow rate is relatively small, this can be said as that the pump efficiency is low. About ⅙ of a diameter of the impeller 54 was employed as the blade groove depth D1. The channel height H is equal to a length of the blade groove depth D1+opposing groove depth D2+a gap between the impeller 54 and the upper wall 52 c (or the bottom wall 52 a). Further, the channel width W is equal to a width of each of the blade grooves 54 b, the opposing groove 52 e, and the opposing groove 52 f.

FIG. 7 is a graph showing a relationship of the D2/D1 and the discharge flow rate. A horizontal axis indicates the D2/D1 and a vertical axis indicates the discharge flow rate (litters/min). FIG. 8 is a graph showing a relationship of the W/H and the discharge flow rate. A horizontal axis indicates the W/H and a vertical axis indicates the discharge flow rate (litters/min). FIG. 9 is a map showing a relationship of the D2/D1, the W/H and the discharge flow rate. As apparent from the graphs of FIGS. 7 and 8, the discharge flow rate becomes maximized at values of the rate D2/D1 of the opposing groove depth D2 relative to the blade groove depth D1 being equal to or less than 0.7 in any case of the rate W/H of the channel width W relative to the channel height H. That is, the pump efficiency becomes optimal at the values of the rate D2/D1 that is equal to or less than 0.7. Further, flow rates that are equal to or greater than ¾ of all cases of maximized discharge flow rate can be maintained from the value of D2/D1 by which the discharge flow rate is maximized and the D2/D1=0.7, and as such, this range can be termed as having relatively fine pump efficiency. Especially in the case where the rate W/H of the channel width W relative to the channel height H is equal to or greater than 0.8 and equal to or less than 1.0, the pump efficiency can be said as especially being superior.

In the simulation results, no incident in which the discharge flow rate drops greatly occurred in a range of the W/H being equal to or greater than 0.7 and equal to or less than 1.2 of the case where the D2/D1 is 0.6, and the pump efficiency can be maintained high. Especially the pump efficiency can be made high when 0.4≤D2/D1≤0.7 and 0.8≤W/H≤1.1 are satisfied.

Next, a reason why the pump efficiency can be improved will be described. In the purge pump 10, as the impeller 54 rotates, vortexes about their center axes along the rotation direction of the impeller are generated in the spaces 57, 59 formed by the blade grooves 54 b and the opposing grooves 52 e, 52 f. FIG. 10 is a simulation result showing the flow of the gas generated in the space 57 between one blade groove 54 b and the opposing groove 52 e (that is, the vortex therein) in a case of D2/D1 =0.6 and W/11=1.0. FIG. 11 is a simulation result showing the flow of the gas generated in the space 57 in a case of D2/D1=0.8 and W/H=1.0. FIG. 12 is a simulation result showing the flow of the gas generated in the space 57 in a case of D2/D1=0.8 and W/H=0.8. In FIGS. 10 to 12, the vortex in the cross-sectional view passing through the rotation axis X of the impeller 54 and the deepest position of the blade groove 54 b is shown. In FIGS. 10 to 12, a left side as seen is a center side of the impeller 54, and a right side is an outer circumferential side of the impeller 54. Further, in FIGS. 10 to 12, arrows are depicted along the vortex flow for easier understanding of the vortex flow.

As shown in FIG. 10, in the case of D2/D1=0.6 and W/H=1.0, the vortex center C1 is located in the blade groove 54 b. On the other hand, as shown in FIG. 11, in the case of D2/D1=0.8 and W/H=1.0, the vortex center C2 is located outside the blade groove 54 b. Similarly in FIG. 12, in the case of D2/D1−0.8 and W/H=0.8, the vortex center C3 is located outside the blade groove 54 b.

In the case where the vortex center is positioned inside the blade groove 54 b, the pump efficiency can be improved. This is because when seen in the cross-sectional view perpendicularly intersecting the rotation direction R of the impeller 54 (that is, in the cross section of FIGS. 10 to 12, which will hereinbelow be termed “perpendicularly-intersecting cross sectional view”), a vicinity of the vortex center has a low gas pressure as compared to a vicinity of the outer circumferential end of the vortex. As a result, when seen in the perpendicularly-intersecting cross sectional view, a flow directed from a high-pressure side to a low-pressure side, that is, from the vicinity of the outer circumferential end of the vortex to the vicinity of the center thereof is generated. The pressure of the gas in the spaces 57, 59 increases as the impeller 54 rotates. Due to this, the gas in the spaces 57, 59 is pressurized as it progresses in the rotation direction R. As a result, the gas in the vicinity of the vortex center attempts to flow to the lower pressure side, that is, in an opposite direction to the rotation direction R of the impeller 54.

FIG. 13 is a diagram that sees an orientation and a flow speed of the gas flow in the vicinity of the center C1 from above in the case of D2/D1−0.6 and W/H=1.0, that is, in the case where the vortex center C1 is positioned in the blade groove 54 b. FIG. 14 is a diagram that sees the orientation and the flow speed of the gas flow in the vicinity of the center C3 from above in the case of D2/D1=0.8 and W/H=0.8, that is, in the case where the vortex center C3 is positioned outside the blade groove 54 b. FIGS. 13 and 14 show a blade 54 a located on the opposite side from the glade groove 54 b in the rotation direction R. A case where a curved line is located on the rotation direction R side than the blade 54 a indicates that the gas is flowing along the rotation direction R and a case where the curved line is located on the opposite side to the rotation direction R indicates that the gas is backflowing with respect to the rotation direction R, and a magnitude of the flow speed is expressed by a distance from the blade 54 a. As shown in FIG. 14, in the case where the vortex center C3 is located outside the blade groove 54 b, the center C3 is located on the blade 54 a on a downstream side. Due to this, the gas that had flown to the center C3 backflows to the lower pressure side, that is, to the opposite side to the rotation direction R, and the pump efficiency thereby decreases.

On the other hand, as shown in FIG. 13, in the case where the vortex center C1 is collated in the blade groove 54 b, the blade 54 a is located on the opposite side of the center C1. Due to this, the gas that had flown to the center C1 is prevented from backflowing to the opposite side of the rotation direction R by the blade groove 54 b. Due to this, the pump efficiency can be improved. In other words, the pump efficiency can be improved by configuring that the rate of the depth of each of the opposing grooves 52 e, 52 f at the intermediate positions excluding both ends of the opposing grooves 52 e, 52 f in the rotation direction R to the depth of each of the blade grooves 52 b at the deepest position of the each of the blade grooves 52 b is set so that the center of the vortexes generated by the blade grooves 54 b and the opposing grooves 52 e, 52 f during the rotation of the impeller 54 are located within the blade grooves 54 b.

Further, since the impeller 54 has the outer circumferential wall 54 c, the flow of the gas flowing toward the outer circumferential direction of the impeller 54 in the spaces 57, 59 is guided, and the gas can thereby be swirled smoothly.

The embodiments of the present invention have been described above in detail, however, these are mere examples and thus do not limit the scope of the claims. The techniques recited in the claims encompass configurations that modify and alter the above-exemplified specific examples.

For example, the shape of the outer circumferential wall 54 c of the impeller 54 is not limited to the shape in the embodiment. For example, as shown in FIG. 15, the outer circumferential wall 54 c may be arranged at a center portion of the impeller 54 in an up and down direction while not being arranged at upper and lower ends thereof. In this case, an upper end of the outer circumferential wall 54 c may be positioned same as or above the vortex center along the up and down direction. A lower end of the outer circumferential wall 54 c may similarly be positioned same as or below the vortex center along the up and down direction. Alternatively, the impeller 54 may not be provided with the outer circumferential wall 54 c.

Further, in the above embodiment, the blades 54 a and the blade grooves 54 b of the impeller 54 are given same shapes on the upper and lower surfaces 54 g, 54 h. However, the shapes of the blades 54 a and the blade grooves 54 b may be different on the upper and lower surfaces 54 g, 54 h. Alternatively, the blades 54 a and the blade grooves 54 b may be arranged only on one of the upper and lower surfaces 54 g, 54 h.

Further, in the above embodiment, the suction port 56 and the discharge port 58 of the pump unit 50 extend in the direction perpendicular to the rotation axis X of the impeller 54. However, the suction port 56 and the discharge port 58 of the pump unit 50 may extend parallel to the rotation axis X.

The “vortex pump” in the disclosure herein is not limited to the purge pump 10, and may be applied in other systems. For example, it may be used as a pump that supplies an exhaust to the suction pipe 80 in an exhaust recirculation (that is, EGR (abbreviation of Exhaust Gas Recirculation)) for circulating the exhaust of the engine 8, mixing it with suctioned air, and supplying the same to a fuel chamber of the engine 8. Further, it may be used as an industrial pump other than for the vehicle.

Further, the technical features described herein and the drawings may technically be useful alone or in various combinations, and are not limited to the combinations as originally claimed. Further; the art described in the description and the drawings may concurrently achieve a plurality of aims, and technical significance thereof resides in achieving any one of such aims. 

1. A vortex pump configured to pump a gas, the pump comprising: a housing comprising a suction channel and a discharge channel; and an impeller housed in the housing and configured to rotate about a rotation axis, wherein the impeller comprises a blade groove region disposed in an outer circumferential portion of at least one end surface of two end surfaces in a rotation axis direction, the blade groove region including a plurality of blades and a plurality of blade grooves, each of the plurality of blade grooves being disposed between adjacent blades, each of the plurality of blade grooves is open at one end surface side, and is closed at the other end surface side, the housing comprises an opposing groove opposing the blade groove region and extending along the rotation direction of the impeller, and a rate of a depth of the opposing groove at an intermediate position excluding both ends of the opposing groove in the rotation direction of the impeller to a depth of each of the blade grooves at the deepest position of the each of the blade grooves is equal to or less than 0.7.
 2. The vortex pump as in claim 1, wherein a rate of a width of each of the blade grooves to a distance from a bottom edge of the each of the blade grooves to a bottom edge of the opposing groove in a cross sectional view passing through the rotation axis of the impeller and the deepest position of the each of the blade grooves is equal to or more than 0.8 and equal to or less than 1.0.
 3. The vortex pump as in claim 1, wherein in a cross-sectional view passing through the rotation axis of the impeller and the deepest position of each of the blade grooves, the rate of the depth of the opposing groove to the depth of the each of the blade grooves is equal to or more than 0.4 and equal to or less than 0.7, and a rate of a width of the each of the blade grooves to a distance from a bottom edge of the each of the blade grooves to a bottom edge of the opposing groove is equal to or more than 0.8 and equal to or less than 1.1.
 4. A vortex pump configured to pump a gas, the pump comprising: a housing comprising a suction channel and a discharge channel; and an impeller housed in the housing and configured to rotate about a rotation axis, wherein the impeller comprises a blade groove region disposed in an outer circumferential portion of at least one end surface of two end surfaces in a rotation axis, the blade groove region including a plurality of blades and a plurality of blade grooves, each of the plurality of blade grooves disposed between adjacent blades, each of the plurality of blade grooves is open at one end surface side, and is closed at the other end surface side, the housing comprises an opposing groove opposing the blade groove region and extending along the rotation direction of the impeller, and a rate of a depth of the opposing groove at an intermediate position excluding both ends of the opposing groove in the rotation direction of the impeller to a depth of each of the blade grooves at the deepest position of the each of the blade groove is set such that a center of a vortex generated by the respective blade grooves and the opposing groove while the impeller rotates is located inside the each of the blade grooves.
 5. The vortex pump as in claim 4, wherein the impeller comprises an outer circumferential wall at an outer circumferential edge, wherein the outer circumferential wall closes the plurality of the blade grooves at an outer circumferential side of the impeller.
 6. The vortex pump as in claim as in claim 1, wherein the impeller comprises an outer circumferential wall at an outer circumferential edge, wherein the outer circumferential wall closes the plurality of the blade grooves at an outer circumferential side of the impeller. 